This invention concerns improvements in and relating to seats, more especially for vehicles.
The invention is concerned with a sprung support structure for attachment to the frame of a vehicle seat in order to provide support for the cushioning and upholstery material of the seat. Such structures are well known, and generally comprise a pair of longitudinally extending side cords formed by paper-wrapped, or plastics-coated wires, and a plurality of transverse wires which extend between and are wrapped around said side cords. The frictional engagement of the transverse wires with the paper or plastics coating of the side cords maintains the transverse wires in an appropriate longitudinal spacing, and in addition, in order to maintain the spacing of the transverse wires at one or more points between the side cords, the transverse wires may be arranged to penetrate one or more further longitudinally extending cords formed of twisted paper, or extruded synthetic plastics material. Such structures form a skeleton for supporting the foamed synthetic plastics material which serves as the cushioning in the modern automobile seat, and may be supported relatively to the frame of the seat by engagement of the said side cords with compression springs located between the side cords and a supporting structure, or by means of tension springs engaging between the said side cords and laterally outwardly spaced frame members of the seat frame. Alternatively, the support structure may simply be embedded in a cushion of moulded synthetic plastics material which is supported in a seat-pan formed of sheet metal.
In order to meet the increasing requirements for automobile seats having a contoured construction, i.e., with a central, flat cushion surface bounded by one or more angled wings, providing lateral or frontal support, cushion structures as referred to above have been developed by extending the said transverse wires beyond the said side cords, at an acute angle to the central portions of said transverse wires, and interconnecting the ends of said transverse wires by means of further longitudinally extending edge wires which define the outer boundary of the seat cushion.
In accordance with one such known construction, as described in U.S.A. Pat. No. 3,639,002, the said transverse wires are wound helically about the said side cords, before being extended to form the side wings of the support structure. Such an arrangement has proved effective in use when supported from a seat frame by means of compression springs, or by being embedded in a foamed synthetic plastics cushion, as described above. However, when such an arrangement is suspended between lateral members of a seat frame by means of tension springs engaging the said side cords, which is a particularly preferred method of installing such a structure in a seat frame, the hitherto known structure has the disadvantage that the helically wound portions of said transverse wires which engage the side cords tend to become unwound as a result of the forces placed on said side cords by the tension springs. This disadvantage renders such a support structure unsuitable for use with this type of spring suspension, or at least requires that the transverse wires be formed of much heavier gauge wire than would otherwise be necessary.